Libs-API Meeting 2025-04-15

tags: `Libs Meetings` `Minutes`

Meeting Link: https://meet.jit.si/rust-libs-meeting-crxoz2at8hiccp7b3ixf89qgxfymlbwr
Attendees: Amanieu, Mara, David, JoshT, The 8472, Chris Denton

Agenda

Triage
Anything else?

Triage

FCPs

11 rust-lang/rust T-libs-api FCPs

merge rust.tf/80437 Tracking Issue for `box_into_inner` - (1 checkboxes left)
merge rust.tf/138498 Implement Deref<Target=ByteStr> for CStr - (3 checkboxes left)
merge rust.tf/106418 Implement `PartialOrd` and `Ord` for `Discriminant` - (2 checkboxes left)
merge rust.tf/130823 Tracking Issue for `non_null_from_ref` - (3 checkboxes left)
merge rust.tf/137280 stabilize ptr::swap_nonoverlapping in const - (3 checkboxes left)
merge rust.tf/122661 Change the desugaring of `assert!` for better error output - (3 checkboxes left)
merge rust.tf/137992 Stabilise `os_string_pathbuf_leak` - (4 checkboxes left)
merge rust.tf/115585 Tracking issue for `cfg_match` - (2 checkboxes left)
merge rust.tf/138016 Added `Clone` implementation for `ChunkBy` - (3 checkboxes left)
merge rust.tf/111137 Tracking Issue for AVX512 intrinsics - (3 checkboxes left)
merge rust.tf/139624 Don't allow flattened format_args in const. - (5 checkboxes left)

dtolnay (1), BurntSushi (7), m-ou-se (5), nikomatsakis (3), joshtriplett (6), Amanieu (6), tmandry (2), scottmcm (2)

(nominated) rust.tf/libs337 Add `((un)checked_)exact_div` methods for integer types

pub const fn checked_exact_div(self, rhs: Self) -> Option<Self>;
pub const fn exact_div(self, rhs: Self) -> Self;
pub unsafe const fn unchecked_exact_div(self, rhs: Self) -> Self;

Amanieu: excited about unchecked_exact_div

Mara: all three seem useful to me. Seems fine to accept this.

David: what optimizations does the unchecked one enable?

Amanieu: https://github.com/rust-lang/libs-team/issues/337#issuecomment-2799431533

David: So, divide by two and then indexing an [u16]?

Amanieu: yup

David: +1 seems great

Amanieu: not sure about exact_div, which panics. questionable.

Mara: leave that one as an open question?

Amanieu: or have exact_div return an Option, remove checked_exact_div.

Amanieu: we can defer that till later.

Accepted

(nominated) rust.tf/libs547 Change ACP process to track unimplemented ACPs

Discussed in last meeting, Amanieu to reply.

(nominated) rust.tf/130703 Tracking Issue for secure random data generation in `std`

Still nominated from last week.

Amanieu: Anything new to discuss?

JoshT: needs more design discussion

Mara: drop nomination, renominate when there's a concrete proposal?

JoshT: probably best

dropped label.

(nominated) rust.tf/137198 Rename `cfg_match!` to `cfg_select!`

Discussed in last meeting, Amanieu to reply.

(nominated) rust.tf/137654 Debug impls of ExtractIf have inconsistent trait bounds

Hashbrown PR: https://github.com/rust-lang/hashbrown/pull/616
Standard library PR: https://github.com/rust-lang/rust/pull/139764 (requires hashbrown release + update)
Beta revert: https://github.com/rust-lang/rust/pull/139765

Amanieu: Still need to look at it.

David: we can also revert. no rush.

(nominated) rust.tf/139224 fix(test): Expose '--no-capture' in favor of `--nocapture`

Mara: Seems like a good improvement. Doesn't result in any warnings for the deprecated one. But needs FCP.

JoshT: +1, this follows common conventions for multi-word command-line options.

Amanieu: delegate all authority to t-testing-devex?

Mara: not sure. did we always vote the same as their FCP?

David: how many FCPs? not many? let's keep it.

Amanieu: previous example: deprecate –logfile

David: we're not stalling them. FCP went through quickly.

Amanieu started FCP

(nominated) rust.tf/139624 Don't allow flattened format_args in const.

FCP ongoing.

(nominated) rust.tf/139865 Stabilize proc_macro::Span::{start,end,line,column,file,local_file}.

David: I think this is ready for FCP

Amanieu: local_file as name?

Mara: file_as_it_exists_on_the_local_file_system was a bit long. local_file is the name in rustc.

Amanieu: why an Option?

Mara: Could come from command line args, for example. Or macro expansion.

Amanieu: Split off file+local_file to a separate stabilization PR? Might be a bit early for those.

Amanieu: not convinced about the name local_file

David: We should expose byte_offset if we expose a way to get the local_file.

David: Might be relevant to get a comment before the field, etc.

Conclusion: don't stabilize file+local_file for now. Do that separate together with byte_offset (and byte_length)?

https://github.com/rust-lang/rust/pull/139865

(waiting on team) rust.tf/136687 Improve the documentation of `Display` and `FromStr`, and their interactions

Amanieu and Josh to bring a proposal back to the team.

(waiting on team) rust.tf/137487 Stabilize `assert_matches` and move it to `core::macros`

(waiting on team) rust.tf/139535 Implement `Default` for raw pointers

(new change proposal) rust.tf/libs572 Add `Cell::get` for `Rc`-like shallow-copying types

For Option-in-Cell, you can already easily do .take(). For Cell<Rc>, you can't do that.

We can implement Clone, or allow .get(), or both, for Cell-of-Rc.

Specific for Rc? Or with some unsafe marker trait?

Amanieu: Inclined to reject. Seems complicated, all this trait business. (Trait for Cell::get)

Amanieu: Cell is in core, Rc is in alloc.

David: CellGet trait seems fine to me. "no funny business" trait for Clone.

Mara: Trait would be similar to the 'cheap to clone' trait?

JoshT: Might also implement the "no funny business" trait for String, even though it's not cheap to clone. But do we want to do that if we're supporting .get() rather than .clone()?

Mara: That allocates, so calls user code in the allocator, which might touch the cell.

JoshT: Implementing the allocator is unsafe.

Amanieu: This is not part of the allocator safety contract.

Sealed/private trait?

We could start with sealed. can always expose it later.

Amanieu: Motivation only mentions Option and Weak, which both implement Default.

Mara: Then we can just require T: Default on a new method.

The 8472: We should ask if that suffices.

Last comment was 3 hours ago. Discussion ongoing.

Amanieu to post a reply.

(new change proposal) rust.tf/libs570 actually checked bitshifts

Discussed in last meeting, Amanieu to reply.

(new change proposal) rust.tf/libs569 ACP: abstract `BufReader::peek`

Amanieu: David had a counterproposal? David, do you remember?

David: That was for a different ACP. http://rust.tf/libs557

(new change proposal) rust.tf/libs568 Implement `Read` and `Write` traits for `BorrowedFd` and `OwnedFd`

We don't have a consensus to implement Read and Write on OwnedFd or BorrowedFd; Josh and 8472 disagree about this.

We have consensus to implement a trait that converts BorrowedFd<'a> to &'a File or similar.

We should also provide an inherent method on BorrowedFd that supports turbofishing the return type.

The 8472 to reply.

(new change proposal) rust.tf/libs562 Add ability to customize STARTUPINFO structure in Command API

(new change proposal) rust.tf/libs557 Add `iter::Peekable::next_unpeek`

Approving peek_slot counterproposal

(new change proposal) rust.tf/libs555 Add `std::io::Seek` instance for `std::io::Take<T>` when `T: Seek`

Approved.

Josh noticed that get_ref allows I/O on many kinds of underlying readers (such as File). Documentation PR to address that: https://github.com/rust-lang/rust/pull/139877

(new change proposal) rust.tf/libs553 Add a "shrink-if-excessive" API to `Vec`

Vec::calc_capacity_growth(&self, reserve: usize) -> usize

The 8472 to ask whether convenience or exposing growth strategy will work for them.

(new change proposal) rust.tf/libs552 Provider-style API for `Context`

Nominated for wg-async

(stalled change proposal) rust.tf/libs364 ACP: Add {Box, Rc, Arc}::map and {Box, Rc, Arc}::try_map

We'd like to see this added to Box, UniqueRc, UniqueArc, instead. And possibly a map_ref function taking Fn(&T) -> U for the opportunistic optimization.

(stalled change proposal) rust.tf/libs181 `Cow::map_borrowed`, `Cow::map_owned`, and `Cow::map`

(stalled change proposal) rust.tf/libs366 Implementing UnixSocketExt traits for solaris/illumos ; starting with the unix_socket_exclbind feature

(stalled change proposal) rust.tf/libs372 ACP: env::home_dir replacement

(stalled change proposal) rust.tf/libs155 Arbitrary alternate flags in `std::fmt::Formatter`

Agree with Mara's rejection of this; closing

(stalled change proposal) rust.tf/libs325 Add macro `static_assert` to perform compile-time assertion checking

(stalled change proposal) rust.tf/libs350 std::slice::from_raw_parts alternative that would accept a null pointer if len == 0 by returning an empty slice

The 8472 to reply.

(stalled change proposal) rust.tf/libs207 `parse_line` method for `Stdin`

(stalled change proposal) rust.tf/libs296 ACP: Designing an alternative `FromStr`

(stalled change proposal) rust.tf/libs194 Fix:Introduce an interface to expose the current `Command` captured env var logic

Generated by fully-automatic-rust-libs-team-triage-meeting-agenda-generator

Libs-API Meeting 2025-04-15

tags: Libs Meetings Minutes

Agenda

Triage

FCPs

(nominated) rust.tf/libs337 Add `((un)checked_)exact_div` methods for integer types

(nominated) rust.tf/libs547 Change ACP process to track unimplemented ACPs

(nominated) rust.tf/130703 Tracking Issue for secure random data generation in `std`

(nominated) rust.tf/137198 Rename `cfg_match!` to `cfg_select!`

(nominated) rust.tf/137654 Debug impls of ExtractIf have inconsistent trait bounds

(nominated) rust.tf/139224 fix(test): Expose '--no-capture' in favor of `--nocapture`

(nominated) rust.tf/139624 Don't allow flattened format_args in const.

(nominated) rust.tf/139865 Stabilize proc_macro::Span::{start,end,line,column,file,local_file}.

(waiting on team) rust.tf/136687 Improve the documentation of `Display` and `FromStr`, and their interactions

(waiting on team) rust.tf/137487 Stabilize `assert_matches` and move it to `core::macros`

(waiting on team) rust.tf/139535 Implement `Default` for raw pointers

(new change proposal) rust.tf/libs572 Add `Cell::get` for `Rc`-like shallow-copying types

(new change proposal) rust.tf/libs570 actually checked bitshifts

(new change proposal) rust.tf/libs569 ACP: abstract `BufReader::peek`

(new change proposal) rust.tf/libs568 Implement `Read` and `Write` traits for `BorrowedFd` and `OwnedFd`

(new change proposal) rust.tf/libs562 Add ability to customize STARTUPINFO structure in Command API

(new change proposal) rust.tf/libs557 Add `iter::Peekable::next_unpeek`

(new change proposal) rust.tf/libs555 Add `std::io::Seek` instance for `std::io::Take<T>` when `T: Seek`

(new change proposal) rust.tf/libs553 Add a "shrink-if-excessive" API to `Vec`

(new change proposal) rust.tf/libs552 Provider-style API for `Context`

(stalled change proposal) rust.tf/libs364 ACP: Add {Box, Rc, Arc}::map and {Box, Rc, Arc}::try_map

(stalled change proposal) rust.tf/libs181 `Cow::map_borrowed`, `Cow::map_owned`, and `Cow::map`

(stalled change proposal) rust.tf/libs366 Implementing UnixSocketExt traits for solaris/illumos ; starting with the unix_socket_exclbind feature

(stalled change proposal) rust.tf/libs372 ACP: env::home_dir replacement

(stalled change proposal) rust.tf/libs155 Arbitrary alternate flags in `std::fmt::Formatter`

(stalled change proposal) rust.tf/libs325 Add macro `static_assert` to perform compile-time assertion checking

(stalled change proposal) rust.tf/libs350 std::slice::from_raw_parts alternative that would accept a null pointer if len == 0 by returning an empty slice

(stalled change proposal) rust.tf/libs207 `parse_line` method for `Stdin`

(stalled change proposal) rust.tf/libs296 ACP: Designing an alternative `FromStr`

(stalled change proposal) rust.tf/libs194 Fix:Introduce an interface to expose the current `Command` captured env var logic

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tags: `Libs Meetings` `Minutes`